US1792320A - High-frequency testing apparatus - Google Patents

Description

1931- J. F. PETERS ETAL ,320

HIGH FREQUENCY TESTING APPARATUS Filed Jan. 2, 1926 WITNESSES: Y J-bmgbgogs &

gym L.Rylandez i ivw WW Patented Feb. 10, 1 931 r -UNITED-STATES;PATENT OFFICE :roniv r. rnrnns, or EDGEWOOD PARK, AND Join; L. RYLANDER, or 1R-WIN',PE1\TN- SYLVANIA, ASSIGNORS TO WESTINGHOUSE ELECTRIC PANY, A CORPORATION OF PENNSYLVANIA.

AND manuracrurtme counrernrnneunivcv 'rnsrmqrarranarus,

Application filed January 2, 1926. Serial No. 78,905.

Our invention relates to a method of, and apparatus for, testing insulated electrical conductors or windin An object of-our invention is to improve the thoroughness with which insulated con-' ductors or windings may be tested without injuring the insulation durin the test by exquency of the testing current will vary 1n the case of a faulty winding by reason of leakage of-current betweenthe turns thereof. The variation of current from normal is therefrom.

detected by means of a resonant circuit contaimng an ammeter orother current-respom sive device, the circuit being so related to the winding under test as .to receive ener by magnetic induction or radiation or hot Fora clearer understandingpf our invdntion and of further objects and advantages thereof, reference shouldbe had to the accompanying drawings, in which Figure 1 is a dia rammatic view of test ing apparatus embo ying the same; Fig. 2 is a similar view of a modification thereof applied to the windings of a dynamo-electric machine; and Fig. 3 is a similar view of another modification.

Referring to Fig; 1, the testing apparatus comprises a big -potential, single-phase transformer 1 energized by a singlebase alternator 2 and adapted to supp y a high-frequency potential to the terminals '3 of a winding ,4 under test. A reactor 5 is connected in the primary circuit of the transv a a former 1 to limit the current "through. the

transformer to a safe value in case the secondary winding is short-circuited by a defect1ve test coil. A condenser 6 is'connected across the terminals of the secondarywinding of the transformer 1', the winding 4 being connected inseries with a spark gap 7 across the terminals of the condenser 6.

' The transformer lmay have a' secondary potential of from 2000 to 20,000 volts or more,

depending upon the type and voltage rating of the apparatus being tested. The spark gap 7 is so adjusted as to break downat somewhat less .than the maximum or peak value of the transrormer voltage, thereby permitting the condenser 6 to discharge through the winding 4. The current through the winding 4 is oscillatory in nature and is highly damped on account of the relatively high resistance of the circuit including the spark gap 7 and winding 4. If desired, a high-frequency alternator or other source of undamped high-frequency current connected directly to the terminals of the winding 4 may be employed, although the oscillatory circuit shown is preferred on account of its simplici ty, low cost and flexibility or case of regulation. I

Anadjustably mounted winding 8 is disposed adjacent to. the winding 4 and is connected in series with a current-responsive device, such as a sensitive ammeter 9, a variable condenser 10 and a variable resistor 11. .The' circuit including the winding 8 and the condenser 10 is adjus'ted,to be 'in resonance with the high-frequency current traversing the windiiig 4.

Thevariable resistor 11 is provided to facilitate the adjustment of the spacing between the windings 4 and 8 for a desired indication upon the ammeter 9. A consider able resistance is initially connected in circuit and the windings 4 and 8 disposed in close proximity to each other. The con.-

denser is then adjusted until the maximum indication of the ammeter,9 shows that the circuitscontaining the windings 4 and 8 are in resonance. The winding 8 is then moved away from the winding 4 and the re sistance 11 is gradually reduced thereby increasing the sharpness of tuning in the coupled circuit. The adjustment is continued in this manner until .the resistance 11 is entirely removed from the circuit and the winding 8 is so related to the winding 4 that the winding 4 under test depend upon the dimensions and insulation of the winding.

If the insulation of the winding breaks down or if a defective winding is connected to the test circuit, the deflection of the instrument 9, instead of being approximately full-scale, is reduced in magnitude, sometimes becoming almost inappreciable The decrease of current in the coupled circuit may result either from the .detuning of the circuits, the change of current in the winding 4, or from both conditions. It will be seen therefore that the method comprises applying a high-frequency current to the winding under test and detecting a variation in the current by means of a resonant circuit of small decrement. The use of a high-frequency test potential prevents a severe burning or injury of the insulation of the winding ,4 in case .a break-down occurs, which would prevent the cause-and the exact location of the fault from being ascertained. Furthermore, the use of a resonant circuit of low decrement provides a sensitive fault-detecting means which is responsive to faults of an exceedingly minute character which could not be discovered by ordinary measuring devices, but which might develop into serious faults under the heat and stress of prolonged service. j

It will be noted that the method comprises in reality a comparison of the characteristics of a plurality of similar windings instead of an exact measurement of the characteristics of a single winding. The main application of the invention is, herefore, to be found in the routine'testing 0 such windings as'form-wound coils for dynamo-elec tric machines or induction apparatus which are manufactured in large quantities and are of similardimensions. Inthecaseofsuch coils, some will be found satisfactory and these may be used as a basis of comparison, as the defective coils will provide a widely different indication uponthe test, instrument 9. y

The transfer of energy between the windings 4 and 8 takes place both by the radiation of energy from the winding 4 and by the magnetic induction between the two windings. When the'windings are in close proximity to each other, the greater proportion of the energy transferred is that contained in the magnetic field, which is so large that a thermo-couple ammeter maybe employed in the coupled circuit. However, if a moresensitive current-responsive device is employed, the apparatus may be so arranged if desired, as to be operated almost entirely by radiated energy.

The invention may be applied to the testing of windings in partially or completely assembled machines, even where the wind- .ings are disposed upon an iron core memher. In Fig. 2 is shown the application of the invention to the testing of. the windings of an armature 15 of a direct-current motor. The armature 15 comprises a plurality of coils 16 connected to the respective commu tator segments 17. The high-frequency testpotential may be applied to the armature windings through the conductors 18 and brushes 19 co-operating with the commutator segments 17.

The resonant detector circuit need not be coupled directl to the winding under test. As shown in th1s figure, an intermediate circuit 20 is disposed between the winding 8 and the winding under test, the circuit 20 comprising a winding 21 adjacent to the armature-15 and a winding 22 ,inductively coupled to the windin 8. The operation of the apparatus is sulastantially the same as' that shown in Fig. 1. Although a plurality of armature windings are connected to each of the commutator segments, after a little practice, an operator -is able to locate the defective winding in the armature by means of the relative positions of the armature winding and the exploring winding 21.

A further modification of the inventionis shown in Fig. 3 in which the winding 4 being tested is connected'in series with a 0011 25 to which the windin 8 is inductively coupled. The operation 0 the apparatus shown in this figure is similar to that shown 1n F 1g.- 1. The circuit including the winding 4, 1s

traversed b ,a damped oscillatory current, of

which the requency depends upon thecharacteristics er the windings .4 and 25 and the capacity of the condenser 6. The detector circuit including the winding 8 is tuned to the same frequency and therefore indicates a defective winding 4 by the altered deflection of the instrument 9.

It will be apparent that the method of testing described aboveis adapted to the testing of windings in large quantities rapidly and expeditiously. Although the apphed potential may be greater than the normal potential for which the windings are designed, a fault in the insulation will not materially damage the windingbecause of the limiting 'character of the supply circuit. Furthermore, it has been found in practice that many slight insulation defects are detected by this method of testing which could not be discovered by any previous method.

The use of the method described in actual practice has resulted in a more uniform and satisfactory grade of insulation of windings and has eflec ted considerable economy by bringing out the fact that certain portions of the windings were provided with too much insulation or too little insulation with respect to the remainder of the windings.

Many other advantages of the improved testing apparatus will be apparent to those skilled in the art and'the above are only men tioned by way of example. i We do not consider that the invention is limited to the apparatus. and the arrangement thereof shown and described in detail. Consequently we desire that the invention should notbe limiteddn scope except as may be indicated in the appended claims.

We claim as our invention 1. The method of testing a winding in position in an electrical translating device which consists in impressing, a high-frequency voltage upon the winding and subjecting a second winding to the electro-magnet-ic influence of the first'winding, adjusting the constants of a circuit includingthe second winding to render the circuit resonant to the frequency of the impressed voltage, and observing the value of the current traversing said circuit when so adjusted.

, 2.111 an ele trical device comprising one or more insul ed windings, means for testing the insul 1011 of said wlndmgs 1n assembled position comprising means for impressing a high-frequency potential on said wind- 4 ings in sequence, and means for receiving the energy radiated from said winding and for indicating the magnitude thereof.

3. In an electrical device comprising a plurality of insulated windings, means for testing the insulation of said windings in assembled position COIIIPIlSlIlg means for impressing a high-frequency potential on said windings, and a circuit for receiving and indicating the magnitude of energy radiated from said winding and including a coil adapted to be moved with respect tosaid electrical decatin vice into energy-receiving relation with respect,t0 said windings.

4. Means for testing the paratus comprising means for energizing a circuittuned to the frequency of the current traversing said conductor including a winding movable with respectto said conductor and energized in accordance with the energy radiating therefrom, and an electrical indi instrument in said circuit.

5. eans for testing the insulation of the insulation of electrical conductors in assembled electrical apwindings in. assembled electrical apparatuscomprising a source of high-frequency curspect to said source, and including a coil'.

adapted to be moved with respect to said win ing for reciving the energy radiated from said winding. 1 U

In testimony whereof wehave hereunto subscribed our names this 29th day of December, 1925.

- JOHN F. PETERS.

JOHN L. RYLANDER.

r so

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